In situ swimming and orientation behavior of spiny lobster (Panulirus argus) postlarvae

Larval dispersal is common in benthic marine organisms, but the environmental cues guiding the final larval stages to settlement habitat remain largely unknown. Caribbean spiny lobster Panulirus argus spend 5 to 12 mo at sea as pelagic phyllosome larvae before transitioning into rapidly swimming and non-feeding puerulus postlarvae. Spiny lobster postlarvae are specialized to seek settlement habitat, making them an ideal model for studying orientation behavior during the transition to benthic environments. We observed the swimming orientation of P. argus in the open ocean during all hours of the day and across tidal phases using a circular behavioral arena deployed at sea. Contrary to laboratory observations of only nocturnal activity, swimming and orientation occurred during both the day and the night in open waters ca. 6 to 8 km offshore in the Florida Straits. Individual postlarvae swam directionally with similar accuracy in all hours. The mean orientation direction was significantly different with tidal phase. Postlarvae oriented to the southeast (163.5) during flood tide, and to the southwest during ebb flow (225.1), placing them on a shoreward trajectory. Postlarval behavior was circatidal, and during ebb tide, innate swimming behavior beneficial to finding settlement habitat was triggered. Postlarvae also oriented relative to the wind, potentially using the sea breeze to orient towards the coast. A change in behavior tied to ubiquitous coastal signals is a strategy likely used by other pelagic larvae searching for a benthic home.